Cardiometrically evaluated NaCl 3% coload versus preload for TURP
A randomized controlled trial
Benign prostatic hyperplasia is common in elderly males, 1 who commonly have different comorbidities especially of the cardiovascular system; making them at risk of many intraoperative complications.
Spinal anaesthesia is regarded as the technique of choice for transurethral resection of the prostate (TURP) procedures.2 Spinal induced hypotension as a consequence of sympathetic blockade is the most common and most important physiologic derangement that occurs due to peripheral vasodilatation.3
Infusion of hypertonic saline (HS) increases plasma osmolality and causes fluid shift from the intracellular to the extracellular space.4 This leads to intravascular volume expansion and thereby improves hemodynamics.5
We hypothesized that a hypertonic solution would limit hypotension occuring with sub-arachnoid block, particularly if given as a ‘coload’, and to combat dilutional hyponatremia induced by absorption of the irrigating fluid during TURP. The main objective of this study aimed to investigate the relevance of time of administration of HS either as a preload or as a coload on hemodynamic parameters in TURP patients, with the aid of electrical cardiometry as a non-invasive monitoring tool.
The primary outcome was to evaluate the effect of HS (preload vs coload) on post spinal hypotension. The secondary outcomes were to assess the need & required dose of vasopressor, post-operative serum Na level as well as any occurring adverse events.
Materials & methods:
Following approval of the trial protocol by the Research Ethics Committee approval number: N-14-2016; a written informed consent form was obtained from all recruited patients, after being given a full explanation about the experimental procedure.
The study was conducted on 100 ASA class I-III patients, aged between 40 & 80 years, candidates for TURP surgeries under subarachnoid block; with exclusion of those having any condition contra-indicating regional anesthesia, with electrolyte imbalance or being allergic to any of the study drugs.
Routine pre-operative evaluation, including history taking, general examination & laboratory investigations, was performed for all patients. Each patient was pre-medicated with Ranitidine 50 mg & Ondansteron 4 mg.
Using computer & sealed envelope randomization, patients were assigned to receive 4 ml/kg of hypertonic saline (NaCL 3%) either pre-operatively over 15-20 min before the induction of spinal anaesthesia Preload group (group P): n=50 or via a 14G cannula at the maximal possible rate at the time of identification of CSF Coload group (group C): n=50.
Routine monitoring consisted of a 5-lead electro-cardiogram with S-T segment analysis, pulse oximetry and non-invasive blood pressure. Spinal anesthesia using 25G spinal needle at the level of L3/4 or L4/5 was administered. A mixed solution of 3–3.5 ml of 0.5% hyperbaric bupivacaine hydrochloride hydrate with 25µ fentanyl in 0.5 ml was used to achieve an anaesthetic level up to the T10 dermatome.
Cases of failed spinal anesthesia were excluded from the analysis and received general anesthesia. Prophylactic ephedrine was not given. TURP was performed using intermittent irrigation system with distilled water which was kept at room temperature and at 60 cm higher than the level of the resectoscope. Oxygen 3-4L/min was supplied to all patients by a face mask throughout the surgical procedure.
Using Non invasive ICON cardiometry, a small sinusoidal current was applied to two standard ECG electrodes at the base of the neck and inferior aspect of the thorax. Two additional electrodes 5 cm inside the stimulating electrodes recorded the changing impedance over that area of the thorax. After cleaning of the skin with alcohol, two gel pad sensors were carefully placed on each side of the thorax along the midaxillary line and two sensors were placed on both sides of the neck directly above the clavicle.
Ephedrine 10 mg IV bolus was administered if SBP ?80% of the baseline or ?100 mm Hg. Bradycardia (HR ?50) was treated with 0.3-0.6 mg of atropine. Vasopressor treatment was repeated if hypotension persists or if it recurs. Smaller decreases in BP (SBP decreases ?20 %) were similarly treated if accompanied by nausea, vomiting, or dizziness. Hypotension was considered present if the patient received at least one dose of vasopressor. An additional rapid bolus infusion of Ringer’s solution was administered at the time of hypotension.
Patients were monitored for signs and symptoms of TURP syndrome (e.g DCL, headache, hypertension, bradycardia, pulmonary edema, seizures), which was managed accordingly in case of occurrence.
A first set of hemodynamic measurements heart rate (HR), systolic blood pressure (SBP), cardiac output (CO) ; systemic vascular resistance (SVR) was recorded as baseline before the HS was given. These measurements were repeated after the induction of spinal anaesthesia every 5 min for the first 30 min and then every 15 min till the end of the surgery.
Approximate size of the prostate obtained by transrectal ultrasonagraphy, duration of the procedure, total volume of irrigating fluid used, number of ephedrine doses required, incidence of any adverse events as well as the post-operative plasma Na level were all recorded.
A previous study 12 showed a decrease in SBP 31 mmHg in patients undergoing TURP surgery after receiving preload with hypertonic saline (with a standard deviation 19 mmHg), we assumed that a change of 35% (11 mmHg) with hypertonic saline as a coload would be clinically significant. So we calculated our sample size based on an assumption of mean differences 11 mmHg between both groups with a standard deviation 18 mmHg using Medcalc software. Taking a study power of 80% and a P value of 0.05, a minimum number of 48 patients was needed in each group. A total number of 100 patients (50 patients in each group) were included to compensate for possible drop-outs.
All normally distributed continuous data were presented as means and (Standard Deviations). Non-normally distributed continuous and ordinal data were expressed as median (range). Categorical data were expressed as number of patients and incidence. Unpaired t-test was used to compare continuous data in the two groups. Repeated measure ANOVA with post-hoc Dunnets test were used to compare changes in continuous variables in relation to the baseline preoperative values e.g. heart rate and blood pressure within each study group. Chi square or Fisher Exact test were used to compare categorical data. For all statistical comparisons a P value of 0.05). (Table 1 ; 2)
The pre- and intra-operative hemodynamic profiles including changes in systolic blood pressure and heart rate were close in the two study groups at the same assessment points, apart from a difference between SBP readings at the 5 min post spinal anesthesia check point being significantly lower in preload group than the coload group (P: 0.049), the most critical time for post spinal hypotension.
The SBP following readings were non-significantly higher in the preload group at all time intervals till the end of surgery with the exception of the 30 min interval reading where the SBP was insignificantly higher in the coload group. Comparing each group with the baseline readings, the SBP was significantly lower than the baseline reading value at 5, 10, 15 min in both groups (P ; 0.001, 0.003 ; 0.036 in group P and 0.002, 0.02 ; 0.025 in group C; respectively). (Fig. 2)
As for HR, no statistically significant differences were detected in between the two groups at any assessment point. Comparing each group with the baseline readings, the HR was significantly lower than the baseline value at 5, 10 min (P ; 0.001) in each group and at 15 min in the preload group (P: 0.014). (Fig. 3)
Baseline and intraoperative CO were recorded and there were no significant differences between both groups regarding the CO readings at all points. While comparing each group with its baseline value, we found that the CO was significantly higher at the 5 ; 10 min check points in the coload group (P: 0.01 ; ; 0.001 respectively), but this significant increase was not sustained to the end of surgery. Whereas for the preload group, the CO was significantly higher than the baseline value at the 10 ; 15 min check points (P ; 0.001). (Table 3)
Regarding the systemic vascular resistance (SVR), there was a significant decrease after spinal anesthesia in the preload group (P ; 0.001) at 5 ; 10 min compared to the coload group. With respect to baseline values, a significant decrease in SVR at 5 ; 10 min was also found in preload group (P ; 0.001) but not in coload group. (Table 4)
Regarding the total consumed dose of ephedrine, the median dose required was significantly greater for patients of the preload group 10.4±6.8 mg in group P vs. 1.2±2.82 mg in group C (P ; 0.001). To be observed again that, more patients in group P required vasopressor support during the procedure (16 vs. only 4 patients in group P ; C respectively).
Concerning the intraoperative adverse effect, no significant differences were noted between both groups regarding the incidence of nausea ; vomiting 4 (8%) vs. 2 (4%) in group P ; C, respectively; P: 0.661 and bradycardia 2 (4%) vs. 1 (2 %) in group P ; C, respectively; P: 1 post spinal anesthesia.
The plasma Na level was measured for patients of both groups postoperatively and all values were within normal with mean Na level 142±3.5 mEq/L for preload group and 138±4 mEq/L for coload group (P value: 0.43).
Spinal anesthesia for transurethral resection of the prostate (TURP) allows the patients to be awake during procedure and thus can help detect earlier signs of TURP syndrome.6
However, the sympathetic blockade, as a major cause of vasodilatation, leads to diminished venous return and hypotension, which is often corrected by administration of I.V. fluids and vasopressors.7 Therefore TURP patients need meticulous monitoring of hemodynamics and fluid therapy.
Electrical cardiometry (Electrical velocimetry) is a type of impedance cardiography, non-invasive and continuously applicable method of cardiac output (CO), stroke volume (SV), and other hemodynamic parameters monitoring. Several studies show a good reliability on its use as a continuous CO monitor as compared to other validated techniques as transthoracic echocardiography (TTE)8,9 ; transesophageal echocardiography.10
Preload and coload are the most commonly used methods for the prevention of spinal induced hypotension. Crystalloid and colloid are both used as preload or coload. Crystalloid is preferred because it’s cheaper and have less effect on coagulation & kidney function than colloid; but as the half-life of crystalloid is 15 – 20 minutes, its effectiveness for prevention of hypotension is questionable. Colloids have the advantage of a long half-life so can more effectively maintain intravascular volume and prevent hypotension. However, colloids are usually expensive, not always available and associated with allergic reactions. Different studies revealed that larger volume of colloid is required to sustain intravascular volume longer than thirty minutes.11
Because osmolality is the driving force for volume distribution, hypertonic saline causes fluid shift from the intracellular space into the intravascular and interstitial spaces.12 Therefore, it increases the plasma volume more than by its own volume. Patients undergoing TURP may develop secondary dilutional hyponatraemia due to systemic absorption of the irrigation fluid. The degree of absorption is related to the time of resection, degree of bleeding and type, volume and pressure of irrigating fluid.13 Prehydration with HS may decrease the degree of dilutional hyponatremia.
The results of the present study has shown that the administration of HS as a coload achieved a significant decrease of post spinal hypotension compared to the preload administration; which was also shown by the fact that the coload group needed lower doses of vasopressor (P